How are merchandise inventory costs determined under a perpetual inventory system?

Use the following information to answer the next 2 questions:

Beginning Inventory January 1st = 100 units x $10 = $1,000

Purchases on January 15th = 100 units x $12 = $1,200

a) Using the perpetual system and FIFO method, what is the Cost of Goods Sold if we sell 125 units on January 20th? Please show work.

b) Using the perpetual system and LIFO method, what is the Cost of Goods Sold if we sell 125 units on January 20th? Please show work.